The term Jumbo first appeared in the mid 80's from Italian collectors to distinguish the earlier larger 3700 from the newer 3800.
Nobody called the Nautilus "Jumbo"prior the introduction of the smaller model.
Even when I started seriously collecting watches in the late 80's, the term "Jumbo" was used mostly by Italians.
Now if you have Patek period literature to corroborate what you are saying, please post.